Hydrogen Breath Test (cont.)

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

How is hydrogen breath testing performed?

Prior to hydrogen breath testing, the patient fasts for at least 12 hours. At the start of the test, the patient blows into and fills a balloon with a breath of air. The concentration of hydrogen is measured in a sample of breath removed from the balloon. The patient then ingests a small amount of the test sugar (lactose, sucrose, sorbitol, fructose, lactulose, etc. depending on the purpose of the test). Additional samples of breath are collected and analyzed for hydrogen every 15 minutes for three and up to five hours.

How are the results of hydrogen breath testing interpreted?

The interpretation of the results of hydrogen breath testing depends on the sugar that is used for testing, and the pattern of hydrogen production after the sugar is ingested.

After ingestion of test doses of the dietary sugars lactose, sucrose, fructose or sorbitol, any production of hydrogen means that there has been a problem with digestion or absorption of the test sugar and that some of the sugar has reached the colon.

When rapid intestinal transit is present, the test dose of non-digestible lactulose reaches the colon more quickly than normally, and, therefore, hydrogen is produced by the colonic bacteria soon after the sugar is ingested.

When bacterial overgrowth of the small bowel is present, ingestion of lactulose results in two separate periods during the test in which hydrogen is produced, an earlier period caused by the bacteria in the small intestine and a later one caused by the bacteria in the colon.

What are the limitations of hydrogen breath testing?

There are several limitations to hydrogen breath testing. For unclear reasons, testing for bacterial overgrowth of the small bowel with lactulose can diagnose only 60% of cases. (This insensitivity of the test may be due in part to the strict criteria that are used for interpreting a test as abnormal. Less strict criteria may diagnose overgrowth more often.) In addition, with bacterial overgrowth there may be an overlap of the early and later periods of hydrogen production that can be misinterpreted as a single period characteristic of rapid intestinal transit. Finally, some normal individuals may have slow transit through the small intestine making prolonged testing - up to 5 hours - necessary, and many individuals are unwilling to undergo such prolonged testing.

Some individuals do not have bacteria that produce hydrogen, and in these individuals hydrogen breath testing is not possible. Most of these individuals have bacteria that produce a different gas, methane. (There also are individuals who produce both hydrogen and methane.) Methane can be measured in the breath just like hydrogen, and the production of methane can be used for diagnosis in the same way as hydrogen. There is much less experience with methane, however, and the production of methane is more complex than the production of hydrogen. Therefore, it is not clear if the pattern of methane production after ingestion of sugars can be interpreted in the same way as hydrogen production, particularly for the diagnosis of bacterial overgrowth.

A pattern of hydrogen production that is typical for bacterial overgrowth does not necessarily mean that an individual's symptoms are caused by the overgrowth. For example, there may be anatomic abnormalities of the small intestine such as narrowing or functional abnormalities in the way the muscle of the small intestine works. These abnormalities can cause symptoms of bloating, distention, pain, and diarrhea themselves, but they also can lead to bacterial overgrowth with its similar symptoms. Therefore, it may be an underlying abnormality that is responsible for the symptoms and not the bacterial overgrowth. The only way to differentiate between the two causes of symptoms-an underlying problem or bacterial overgrowth - is to treat and eradicate the bacteria. If the symptoms disappear, then it is more likely that it is the overgrowth rather than the underlying abnormality that is responsible for the symptoms.

Any condition that results in the delivery of undigested or unabsorbed food to the colon may result in abnormal breath tests when dietary sugars are used for testing. Both pancreatic insufficiency and celiac sprue can cause abnormal breath tests, in the former instance because pancreatic enzymes that are necessary for the digestion of carbohydrates are missing, and in the latter instance because the lining of the small intestine is destroyed, and digested food cannot be absorbed. It may be necessary to exclude these causes of abnormal breath tests by additional tests-pancreatic function tests and small intestinal biopsy.